1. Field of the Invention
The present invention relates generally to an apparatus for aligning an optical source with an optical fiber and an optical source module having the same.
2. Description of the Related Art
Generally, an optical source module having an optical source aligned with an optical fiber therein can be applied to any optical part which transmits/receives light. Particular examples include a pump laser diode (LD) module, a semiconductor optical amplifier module, a 2.5-Gbit transmission/reception module, and a 155-Mbit transmission/reception module, which require high optical coupling efficiency.
A conventional apparatus for aligning an optical source with an optical fiber includes a laser diode installed on a substrate, a photo diode (PD) aligned with the laser diode on the substrate, an optical fiber aligned with the laser diode, a ferrule having the optical fiber inserted thereinto, and a saddle fixing the ferrule.
The laser diode is aligned with the optical fiber in the following procedure. The laser diode is first fixed on the substrate and the optical fiber is fixed to the ferrule by soldering. The saddle is in turn fixed on the substrate. For alignment, an external driver (not shown) feeds current through the laser diode and then light is emitted from the laser diode. The displacement of the ferrule is regulated so that the optical fiber can receive a maximum of the emitted light. At a maximum light receiving position, the saddle is welded to the ferrule. Here, welding-caused deformation should be within an alignment error range. For application of the above mechanism to an optical fiber amplifier, the photodiode is provided to measure the intensity of the light emitted from the laser diode and feed back the measurement to the external driver, to thereby control the output of the laser diode.
To allow the optical fiber to obtain a high optical coupling efficiency from the laser diode, an end of the optical fiber is formed into a lens of the same shape as the far field pattern of the laser diode and aligned on multi-axes with the laser diode. In this case, the smallest alignment error range on an axis should be maintained at or below about 0.2 .mu.m.
This conventional aligning apparatus, however, has the distinctive shortcoming of thermal expansion and contraction associated with welding. More specifically, the portion at the center of the saddle welded with the ferrule seriously incurs welding deformation to the saddle though welding the bottom of the saddle to the substrate causes no deformation.
An alignment error range along a vertical axis (y-axis) is the smallest, about 0.2 .mu.m or less. Welding a saddle with a ferrule at welding points after alignment of an optical source with an optical fiber deforms the saddle downward as indicated by reference numeral due to welding heat. That is, thermal deformation of about 10-20 .mu.m occurs along the y-axis, negatively influencing optical coupling efficiency. A saddle is also thermally deformed by about 5-10 .mu.m exceeding an alignment error range, along the y-axis.
Examples of optical fiber alignment apparatus and methods of the conventional art are seen in the following U.S. Patents. U.S. Pat. No. 4,850,671, to Finzel, entitled Connector Device For Light Waveguides, describes a connector device for light waveguides having a fixing part and guide parts of various structures.
U.S. Pat. No. 4,854,677, to Ebata et al., entitled Optical Fiber Alignment And Fixing Method And Apparatus Therefor, describes a translation stage having a fixture in the form of a saddle for holding an optical fiber. The saddle has stepped portions.
U.S. Pat. No. 4,856,866, to Freeman et al., entitled Optical Fiber Connecting Means, describes an aligned plug optical fiber connector.
U.S. Pat. No. 4,915,472, to Liu, entitled Optical Fiber Terminal Plug Connectors, describes an optical fiber terminal plug connector for aligning two optical fibers.
U.S. Pat. No. 5,367,140, to Jouaneh et al., entitled Method For Laser Welding Of Optical Packages, describes an optical package having a base, a laser and a soldered optical fiber held in place by a saddle.
U.S. Pat. No. 5,631,989, to Koren et al., entitled Fiber And Active Optical Device Interconnection Assembly, describes a connector assembly for coupling an optical fiber to an active optical device.
U.S. Pat. No. 5,570,444, to Janssen et al., entitled Method Of Optically Coupling Fibers To Injection Lasers, describes an arrangement for aligning an optical fiber with an injection laser using a deformable saddle having two shoulders which support a slit rod holding the optical fiber.
However, these conventional methods and apparatus do not avoid the above-described problems associated with soldering a saddle to a substrate.